This application claims the benefit of Korean Application No. 2001-64910, filed Oct. 20, 2001, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates, generally, to a display apparatus, and more particularly, to a display apparatus having a power supply capable of lowering power consumption effectively in a power saving mode.
2. Description of the Related Art
Generally, in a display apparatus, a power supply supplies electric power to components such as a deflection circuit, a high voltage circuit, etc., respectively. Recently, technology related to an SMPS (Switched Mode Power Supply) has been rapidly developing. An SMPS is small, light and effective compared to a linear power supply.
A conventional SMPS 150, as shown in FIG. 5, comprises a power supplying part 101, a transformer (105, 105a, 105b, 106 and 106a), a feedback voltage sensing part 109 sensing a voltage applied to a secondary coil 106, and a power driving part 110 supplying a square wave AC (Alternating Current) voltage to a primary coil 105 on the basis of a synchronous signal applied from a video card (not shown).
Referring to FIG. 5, an operation of the SMPS 150 is described hereinbelow. First, commercial AC power of 110V or 220V is supplied to the SMPS 150 by the power supplying part 101. The commercial AC power is converted into a DC (Direct Current) voltage xe2x80x9cB+xe2x80x9d through a rectifier 102 and a capacitor 102a. The DC voltage xe2x80x9cB+xe2x80x9d generates a starting current based on a starting resistor 103, so as to operate the power driving part 110. As the power driving part 110 is operated, a PWM (Pulse Width Modulation) control signal S1 is applied to the primary coil 105. The PWM control signal S1 is generated from a power driver (to be described later) provided inside the power driving part 110. Further, the PWM control signal S1 generates an AC voltage in the primary coil 105, and therefore an AC voltage is induced in the secondary coils 106 and 106a and supplied to driving circuits (not shown) inside a display apparatus. The induced AC voltage of the secondary coil 106a goes through a diode 112 and is stabilized by a regulator 113, thus being applied to a control part 114.
Referring to FIG. 6, the power driving part 110 includes a free-run frequency generator 131 generating a synchronous signal by itself in a power saving mode in which the synchronous signal is not received from a video card (not shown) The power driving part 110 also includes a selecting part 132 selecting one of the synchronous signal received from the video card (not shown) in normal mode, and the synchronous signal received from the free-run frequency generator 131 in the power saving mode. In addition, the power driving part 110 includes a power driver 135 outputting the PWM control signal S1 in response to the synchronous signal, a power transistor 138 which is switched on/off according to the PWM control signal S1 outputted from the power driver 135, and a feedback voltage regulating part 134 transmitting a voltage-regulating signal S2 to the power driver 135. The duty ratio of the voltage-regulating signal S2 is regulated by comparing a feedback voltage with an output voltage of the power transistor 138 The drain of the power transistor 138 is coupled to drive, and the source of the power transistor 138 is coupled to resistor 139.
Referring again to FIG. 5, in the power saving mode, the control part 114 cuts off the output of the secondary coil 106 supplied to each driving circuit by switching off a load connection switch 115, thus lowering power consumption. Accordingly, as the output of the secondary coil 106 is cut off from the other components, the load thereof is decreased and the feedback voltage is reduced. On the basis of the reduced feedback voltage, the feedback voltage regulating part 134 of the power driving part 110 transmits the voltage-regulating signal S2 to the power driver 135. Then, the power driver 135 transmits the PWM control signal S1 to the power transistor 138 in response to the synchronous signal generated from the free-run frequency generator 131. According to the PWM control signal S1, the power transistor 138 is switched on/off, and thus an AC voltage is supplied to the primary coil 105. At this time, the control part 114 and the power driving part 110 consume 0.2 Watt and 1 Watt or more, respectively, of power. Furthermore, because power consumption due to a leakage current at the starting resistor 103 is added to the above power consumption, total power consumption is at least 2 Watts or more.
Thus, in order to lower the power consumption in the power saving mode, lowering the power consumption of the power driving part 110 is effective because the power consumption of the power driving part 110 is relatively higher than that of the control part 114. As a method for lowering the power consumption of the power driving part 110 in the power saving mode, there is proposed a method of lowering the frequency of the free-run frequency generator 131 and increasing the resistance of the starting resistor 103.
However, if the frequency of the free-run frequency generator 131 is lowered, the transformer makes a noise. Further, if the resistance of the starting resistor 103 is increased, the starting current is decreased and the minimum on-duty of the PWM control signal for driving the transformer is not secured. Accordingly, the output voltage of the transformer is unstable, thus making the operations of the power driving part 110 and the control part 114 unstable.
Accordingly, the present invention has been made keeping in mind the above-described shortcomings and user""s need.
An aspect of the present invention is to provide a display apparatus having a power supply minimizing power consumption at a power saving mode by operating a power driving part with a synthetic synchronous signal, securing stable operations of a control part and the power driving part.
This and other aspects of the present invention are accomplished by a display apparatus of the present invention. The display apparatus of the present invention inlcudes a power supply comprising a commercial AC power supplying part, a transformer having a primary coil and a secondary coil and supplying an AC voltage to driving circuits, and a feedback voltage sensing part sensing a load of the secondary coil. The power supply of the display apparatus of the present invention also comprises a power mode information part providing information for determining a normal mode or a power saving mode according to an input of a synchronous signal; a power driving part including a power driver generating a power regulating signal according to a synchronous signal on the basis of a feedback voltage sensed by the feedback voltage sensing part in the normal mode, and an idle power driver generating a power saving voltage on the basis of a synchronous signal which is made by synthesizing different frequency signals in the power saving mode; an idle switching part turning on/off the idle power driver; and a control part cutting off the feedback voltage applied to the power driver and controlling the idle switching part so as to operate the idle power driver in the power saving mode.
The power driving part includes a power transistor connected to the primary coil, and the idle power driver includes a plurality of sawtooth generators respectively generating sawtooth signals with several tens of hertz (Hz) and several tens of kilohertz (KHz), a plurality of comparators processing the sawtooth signals and outputting square wave signals having different pulse widths, and an AND gate logically synthesizing the square wave signals outputted from the comparators and supplying the synthetic square wave signal to the power transistor.
The display apparatus further comprises an OR gate provided between the power driver and the power transistor, logically OR-ing output signals of the power driver and the idle power driver, and supplying the result to the power transistor.
The sawtooth generator generating the sawtooth signal of several tens of hertz (Hz) is driven on the basis of the DC voltage of the primary coil, and the sawtooth generator generating the sawtooth signal of several tens of kilohertz (KHz) is driven on the basis of the driving voltage of the power driving part.
The power driving part further includes an inverter provided between the power driver and the AND gate so as to suspend the operation of the idle power driver in the normal mode, and the power driving part outputs a power-saving off signal to the AND gate through the inverter when the power saving mode changes to the normal mode.
The idle switching part includes a photocoupler and a power-saving off transistor turned on together with the photocoupler and cutting off the DC voltage supplied to the comparator receiving the several tens of hertz (Hz) sawtooth signal.
The power driving part further includes a feedback voltage regulating part transmitting a feedback regulating signal after comparing a voltage sensed by a sensing resistor with a feedback voltage sensed by the feedback voltage sensing part, and the idle switching part further includes a feedback-cutoff transistor operating contrary to the power-saving off transistor and cutting on/off the feedback voltage supplied to the feedback voltage regulating part.
The control part outputs a load-off signal switching off a connection between the secondary coil and each driving circuit after operating the idle switching part after a predetermined time lapse at the beginning of the power saving mode.
The control part turns off the idle switching part after connecting the secondary coil with each driving circuit when the power saving mode changes to the normal mode.
The power mode information part includes a video card turning on/off the synchronous signal applied to the power driver according to the normal mode or the power saving mode.
Moreover, the present invention comprises a power supply for a display apparatus. The power supply of the present invention comprises a power driving part receiving a synchronous signal. The power driving part comprises a power driver generating a power regulating signal according to a synchronous signal on the basis of a feedback voltage sensed by a feedback voltage sensing part in the normal mode; and an idle power driver generating a power saving voltage on the basis of a synchronous signal which is made by synthesizing different frequency signals in the power saving mode. The power supply of the present invention further comprises an idle switching part, coupled to the power driving part, turning on/off the idle power driver. In addition, the power supply of the present invention comprises a control part, coupled to the idle switching part, cutting off the feedback voltage applied to the power driver and controlling the idle switching part so as to operate the idle power driver in the power saving mode.
Moreover, the present invention comprises a method of a power supply for a display apparatus. The method of the present invention comprises receiving by a power driving part a synchronous signal, generating by a power driver a power regulating signal according to a synchronous signal on the basis of a feedback voltage sensed by a feedback voltage sensing part in a normal mode, cutting off the feedback voltage applied to the power driver in the power saving mode, and generating a power saving voltage on the basis of a synchronous signal which is made by synthesizing different frequency signals in the power saving mode.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.